During the operation of the process plant, it is crucial to the functioning of the plant that all flange connections be tight. It is obvious that even small leaks from pipelines carrying flammable gases at high pressures are undesirable and highly dangerous. Thus the internal inspection routines for a process plant comprise both a periodic inspection of flanges and a pressure testing plan for the pipes.
In conventional pressure testing of piping installations, the pipes are first drained of their contents, whereupon the piping installation is filled with a non-flammable gas such as nitrogen and pumped up to a pressure in considerable excess of the normal operating pressure of the installation. If the pressure in the installation does not fall subsequent to the filling, the installation is pressure tight. In the opposite case, there is at least one leak that must be located and repaired before the installation is pressure tested again. Locating leaks may be highly time consuming, even though some equipment is available for this purpose. The consumption of non-flammable gas when using this conventional pressure testing method is relatively high. The amount of time spent on gas filling and building up pressure is also considerable.
In order to overcome the unfavourable aspects of conventional pressure testing, several methods have been proposed in which flange connections may be tested individually, and where in some methods it is also possible to monitor the individual flange connections for leaks.
Norwegian patent 175 832 describes a method of testing and monitoring which has gained extensive use. According to the patent, a gasket is provided with bores that connect the initially mentioned annuli positioned between the end faces of the gasket in the grooves in the f flange halves, with an external piping connection. By filling pressurised gas in the annuli and then monitoring the pressure value, it may be determined whether the flange connection is tight or not. Likewise, the flange connection may be connected to a monitoring apparatus that is known per se, e.g. a pressure switch, which is designed to transmit a signal upon a pressure increase in the annuli during operation. Thus is achieved a leakage warning that may be attributed to an individual flange connection.
Said piping connection connected to the external cylindrical surface of the gasket runs through the annular gap formed between the flange halves when two flange halves of the type in question are joined. The gap, which according to the standardised flange design is approximately constant across a wide range of dimensions, is well suited for providing access to the external periphery of the seal.
Some types of flange connections however are not provided with gaps sufficiently dimensioned to allow the connection of a pipe to the gasket. According to prior art, it is not possible to use piping connections according to Norwegian patent 175 832 on flange connections of this type.